The present invention relates to fluid flow measuring devices, methods for determining fluid flow rates, and more specifically, fluid flow measuring devices for determining fluid flow rates in soils.
Determining the rate of fluid flow, or fluid flux, in an earthen profile is important to many scientific and engineering disciplines, as well as to environmental, agricultural and other industries who are dependant, at least in part, on the mechanics and dynamics of water in a given earthen profile. For example, the agriculture/horticultural industry is greatly benefitted when the groundwater flux of soil can be accurately monitored such that irrigation can be controlled to optimize the rate of plant growth. Moreover, the associated leaching of minerals and nutrients could be monitored to predict the needs of crops at the root zone, particularly shallow rooted crops such as potatoes where leaching rates are the greatest. Still further, in the landfill industry, and in particular, hazardous waste sites which use impermeable layers (e.g. asphalt or compacted clay) to retard or prevent seepage of hazardous waste into the soil and ultimately the water supply, the monitoring of the performance of the respective layers is imperative. Yet further, for recreational facilities, such as golf courses, the greatest expenditure for the grounds is the construction and maintenance of the greens. Accordingly, monitoring the water flux below the greens is important to establish the water and nutrient needs for the delicate grasses used.
Fluid flow rates for the applications discussed above deal with fluid flows in unsaturated soils (commonly referred to as the xe2x80x9cvadose zonexe2x80x9d). Groundwater and other fluids that enter the soil percolate from a soil-moisture zone through the unsaturated zone to an aquifer (a stratum of permeable rock beneath the earthen profile that stores water). The fluids are constantly in motion and the flow through the unsaturated zone is complicated with the actual rate dependent on the transmissivity through the soil (based on factors of soil composition, atmospheric and other pressure gradients, interstices configuration, etc.) and storage capacity of the aquifer. Accordingly, a wide range of flow rates may occur in the soil over a period of time. For example, flow rates are normally high during the rainy season in relative comparison to that seen during the dry season.
However, as compared to the rate of surface water flow, soil flow rates are relatively slow which makes accurate measurements of same difficult. Heretofore, devices designed to measure fluid flow rates in soils were seen as cost prohibitive for many applications, and largely ineffective for measuring ranges of flow rates. For example, hazardous waste sites use expensive drainage lysimeter systems where drainage flow rates of less than 50 mm/year are of interest.
One prior art means for measuring fluid flow rates is thermal dissipation technology. This technology is based on the principle that thermal energy from a heat source in a fluid medium traveling away from the heat source dissipates heat in the direction of the fluid flow quicker than against the direction of fluid flow. However, prior art devices incorporating this technology are employed for measuring ranges of fluid flow rates not occurring in unsaturated soils.
Therefore, a need exists to provide an inexpensive fluid flow measuring device for measuring fluid flow rates occurring in unsaturated soils which avoid the prior art deficiencies noted above.